Provided is a method for producing low-substituted hydroxypropylcellulose in which depolymerization capable of achieving a target viscosity in a short time is carried out safely after an etherification reaction step. More specifically, provided is a method for producing low-substituted hydroxypropylcellulose having a degree of hydroxypropoxy substitution of from 9.5 to 16.0% by weight, comprising at least a step of reacting alkali cellulose with an etherifying agent and a step of carrying out depolymerization after the reaction.